Semiconductor device and manufacturing method thereof

ABSTRACT

In a method of manufacturing a semiconductor device, a fin structure having a bottom portion, an intermediate portion disposed over the bottom portion and an upper portion disposed over the intermediate portion is formed. The intermediate portion is removed at a source/drain region of the fin structure, thereby forming a space between the bottom portion and the upper portion. An insulating layer is formed in the space. A source/drain contact layer is formed over the upper portion. The source/drain contact layer is separated by the insulating layer from the bottom portion of the fin structure.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 16/585,313filed Sep. 27, 2019, now U.S. Pat. No. 10,943,832, which is a divisionalof application Ser. No. 16/201,694 filed Nov. 27, 2018, no U.S. Pat. No.10,770,358, which is a divisional application of application Ser. No.15/798,227 filed on Oct. 30, 2017, now U.S. Pat. No. 10,867,866, theentire contents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to a semiconductor integrated circuit, and moreparticularly to a semiconductor device having gate-all-around fieldeffect transistors and their manufacturing process.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as amulti-gate field effect transistor (FET), including a fin FET (FinFET)and a gate-all-around (GAA) FET. In a GAA FET, a channel region isformed by a semiconductor wire wrapped with a gate dielectric layer anda gate electrode layer. Because the gate structure surrounds (wraps) thechannel region on all lateral surfaces, the transistor essentially hasfour gates controlling the current through the channel region.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A and 1B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 2A and 2B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 3A and 3B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 4A and 4B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 5A and 5B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 6A and 6B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 7A and 7B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 8A and 8B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 9A, 9B and 9C show one of the various stages of sequentialprocesses for manufacturing a semiconductor device having a GAA FETaccording to an embodiment of the present disclosure.

FIGS. 10A and 10B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 11A and 11B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 12A and 12B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 13A and 13B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 14A and 14B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 15A and 15B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure.

FIGS. 16A, 16B and 16C show one of the various stages of sequentialprocesses for manufacturing a semiconductor device having a GAA FETaccording to an embodiment of the present disclosure.

FIGS. 17A, 17B and 17C show one of the various stages of sequentialprocesses for manufacturing a semiconductor device having a GAA FETaccording to an embodiment of the present disclosure.

FIGS. 18A and 18B show a semiconductor device having a GAA FET accordingto another embodiment of the present disclosure.

FIGS. 19A and 19B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toanother embodiment of the present disclosure.

FIGS. 20A and 20B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toanother embodiment of the present disclosure.

FIGS. 21A, 21B and 21C show one of the various stages of sequentialprocesses for manufacturing a semiconductor device having a GAA FETaccording to another embodiment of the present disclosure.

FIGS. 22A and 22B show a semiconductor device having a GAA FET accordingto another embodiment of the present disclosure.

FIGS. 23A and 23B show a semiconductor device having a GAA FET accordingto another embodiment of the present disclosure.

FIGS. 24A and 24B show a semiconductor device having a FinFET accordingto another embodiment of the present disclosure.

FIGS. 25A and 25B are experimental and simulation results showing theeffects of the present embodiments.

FIGS. 26A and 26B are experimental and simulation results showing theeffects of the present embodiments.

FIGS. 27A and 27B are experimental and simulation results showing theeffects of the present embodiments.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.”

A gate-all-around FET (GAA-FET) generally includes one or moresemiconductor wires having a channel region and source/drain regionsdisposed on both ends of the channel region. To manufacture thesemiconductor wire(s), stacked layers of different semiconductormaterials, one(s) of which is/are a sacrificial layer, are formed, andthen the sacrificial layer(s) is/are removed, thereby leavingsemiconductor wire(s). In the source/drain regions, the sacrificiallayer may remain at the bottom of the stacked layers, which would causea parasitic transistor. The parasitic transistor in a GAA FET adverselyaffects an off-state leakage current. In particular, when a narrow-bandgap material, such as Ge, is used as a channel material, the off-stateleakage current becomes more problematic.

The present disclosure provides a semiconductor device, such as a GAAFET, which can reduce the off-state leakage current.

FIGS. 1A-17B show sequential processes for manufacturing a semiconductordevice having a GAA FET according to an embodiment of the presentdisclosure. It is understood that additional operations can be providedbefore, during, and after processes shown by FIGS. 1A-17B, and some ofthe operations described below can be replaced or eliminated, foradditional embodiments of the method. The order of theoperations/processes may be interchangeable. In FIGS. 1A-17B, the “B”figures (FIGS. 1B, 2B, . . . ) show plan views (viewed from above) andthe “A” figures (FIGS. 1A, 2B, . . . ) show cross sectional views alongthe Y direction (lines Y1-Y1 or Y2-Y2).

FIGS. 1A and 1B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure. FIG. 1A is a cross sectionalview corresponding to line Y1-Y1 of FIG. 1B.

As shown in FIGS. 1A and 1B, a first semiconductor layer 20 isepitaxially formed over a substrate 10, and a second semiconductor layer25 is epitaxially formed over the first semiconductor layer 20.

In one embodiment, substrate 10 includes a single crystallinesemiconductor layer on at least its surface portion. The substrate 10may comprise a single crystalline semiconductor material such as, butnot limited to Si, Ge, SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs,GaSbP, GaAsSb and InP. In one embodiment, the substrate 10 is made ofSi.

The substrate 10 may include in its surface region, one or more bufferlayers (not shown). The buffer layers can serve to gradually change thelattice constant from that of the substrate to that of the source/drainregions. The buffer layers may be formed from epitaxially grown singlecrystalline semiconductor materials such as, but not limited to Si, Ge,GeSn, SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs, GaSbP, GaAsSb, GaN,GaP, and InP. In a particular embodiment, the substrate 10 comprisessilicon germanium (SiGe) buffer layers epitaxially grown on the siliconsubstrate 10. The germanium concentration of the SiGe buffer layers mayincrease from 30 atomic % germanium for the bottom-most buffer layer to70 atomic % germanium for the top-most buffer layer. The substrate 10may include various regions that have been suitably doped withimpurities (e.g., p-type or n-type conductivity).

The first semiconductor layer 20, which is a sacrificial layer, includesa semiconductor material different from the substrate 10. In someembodiments, the first semiconductor layer 20 is made of epitaxiallygrown single crystalline semiconductor materials such as, but notlimited to Si, Ge, GeSn, SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs,GaSbP, GaAsSb, GaN, GaP, and InP. In one embodiment, the firstsemiconductor layer is made of Si_(x)Ge_(1-x), where 0.1<x<0.9(hereinafter may be referred simply to SiGe). The thickness of the firstsemiconductor layer 20 is in a range from about 5 nm to about 30 nm insome embodiments, and is in a range from about 10 nm to about 20 nm inother embodiments.

The second semiconductor layer 25 includes a semiconductor materialdifferent from the first semiconductor layer 20. In some embodiments,the second semiconductor layer 25 is made of epitaxially grown singlecrystalline semiconductor materials such as, but not limited to Si, Ge,GeSn, SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs, GaSbP, GaAsSb, GaN,GaP, and InP. In one embodiment, the second semiconductor layer is madeof Si_(y)Ge_(1-y), where x<y. In a certain embodiment, the secondsemiconductor layer is made of Si. The thickness of the secondsemiconductor layer 25 is in a range from about 10 nm to about 80 nm insome embodiments, and is in a range from about 15 nm to about 30 nm inother embodiments.

FIGS. 2A and 2B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure. FIG. 2A is a cross sectionalview corresponding to line Y1-Y1 of FIG. 2B.

Fin structures 21 are formed by one or more photolithography and etchingoperations, as shown in FIGS. 2A and 2B. The fin structures 21 may bepatterned by any suitable method. For example, the fin structures may bepatterned using one or more photolithography processes, includingdouble-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a dummy layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patterneddummy layer using a self-aligned process. The dummy layer is thenremoved, and the remaining spacers may then be used to pattern the fins.

In other embodiments, the fin structures can be patterned by using ahard mask pattern 22 as an etching mask. In some embodiments, the hardmask pattern 22 includes a first mask layer and a second mask layerdisposed on the first mask layer. The first mask layer is a pad oxidelayer made of a silicon oxide, which can be formed by a thermaloxidation. The second mask layer is made of a silicon nitride (SiN),which is formed by chemical vapor deposition (CVD), including lowpressure CVD (LPCVD) and plasma enhanced CVD (PECVD), physical vapordeposition (PVD), atomic layer deposition (ALD), or other suitableprocess. The deposited hard mask layer is patterned into a hard maskpattern 22 by using patterning operations including photo-lithographyand etching. Then, the second semiconductor layer 25, the firstsemiconductor layer 20 and the substrate 10 are patterned by using thehard mask pattern into fin structures 21, both extending in the Xdirection. In FIGS. 2A and 2B, two fin structures 21 are arranged in theY direction. But the number of the fin structures is not limited to two,and may include three or more. In some embodiments, one or more dummyfin structures are formed on both sides of the fin structures to improvepattern fidelity in the patterning operations. As shown in FIG. 2A, eachof the fin structures has a bottom portion 11 (a part of the substrate10), an intermediate portion 20 (the first semiconductor layer) disposedover the bottom portion and an upper portion 25 (the secondsemiconductor layer) disposed over the intermediate portion.

The width of the upper portion of the fin structure along the Ydirection is in a range from about 5 nm to about 40 nm in someembodiments, and is in a range from about 10 nm to about 20 nm in otherembodiments. The height along the Z direction of the fin structure is ina range from about 100 nm to about 200 nm in some embodiments.

FIGS. 3A and 3B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure. FIG. 3A is a cross sectionalview corresponding to line Y1-Y1 of FIG. 3B.

After the fin structures 21 are formed, a first insulating materiallayer 29 including one or more layers of insulating material is formedover the substrate 10 so that the fin structures 21 are fully embeddedin the first insulating material layer 29. The insulating material forthe first insulating material layer 29 may include silicon oxide,silicon nitride, silicon oxynitride (SiON), SiCN, fluorine-dopedsilicate glass (FSG), or a low-K dielectric material, formed by LPCVD(low pressure chemical vapor deposition), plasma-CVD or flowable CVD orany other suitable film formation methods. In some embodiments, thefirst insulating material layer 29 is made of silicon oxide. An annealoperation may be performed after the formation of the first insulatingmaterial layer 29. Then, a planarization operation, such as a chemicalmechanical polishing (CMP) method and/or an etch-back method, isperformed such that the hard mask patterns 22 are removed and uppersurfaces of the second semiconductor layer 25 are exposed from the firstinsulating material layer 29 as shown in FIG. 3A.

In some embodiments, one or more fin liner layers 28 are formed over thefin structures before forming the first insulating material layer 29.The fin liner layer 28 may be made of SiN or a silicon nitride-basedmaterial (e.g., SiON or SiCN).

FIGS. 4A and 4B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure. FIG. 4A is a cross sectionalview corresponding to line Y1-Y1 of FIG. 4B.

Then, as shown in FIG. 4A, the first insulating material layer 29 isrecessed to form a first isolation insulating layer 30 so that the upperportions of the fin structures 21 are exposed. With this operation, thefin structures 21 are electrically separated from each other by thefirst isolation insulating layer 30, which is also called a shallowtrench isolation (STI). After the recess etching, the height H₁ of theexposed fin structures is in a range from about 40 nm to about 100 nm insome embodiments, and is in a range from about 60 nm to about 80 nm inother embodiments.

As shown in FIG. 4A, a part of the first semiconductor layer 20 isexposed from the first isolation insulating layer 30. In otherembodiments, the first semiconductor layer 20 is fully exposed from theisolation insulating layer 30.

FIGS. 5A and 5B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure. FIG. 5A is a cross sectionalview corresponding to line Y2-Y2 of FIG. 5B.

After the first isolation insulating layer 30 is formed, a dummy gatestructure 40 is formed, as shown in FIGS. 5A and 5B. The dummy gatestructure 40 includes a dummy gate dielectric layer and a dummy gateelectrode layer. The dummy gate dielectric layer includes one or morelayers of insulating material, such as a silicon oxide-based material.In one embodiment, silicon oxide formed by CVD is used. The thickness ofthe dummy gate dielectric layer is in a range from about 1 nm to about 5nm in some embodiments.

The dummy gate structure 40 is formed by first blanket depositing thedummy gate dielectric layer over the exposed fin structures 21 and theupper surface of the first isolation insulating layer 30. A dummy gateelectrode layer is then blanket deposited on the dummy gate dielectriclayer, such that the fin structures are fully embedded in the dummy gateelectrode layer. The dummy gate electrode layer includes silicon such aspolycrystalline silicon (polysilicon) or amorphous silicon. In someembodiments, the dummy gate electrode layer is made of polysilicon. Thethickness of the dummy gate electrode layer is in a range from about 100nm to about 300 nm in some embodiments. In some embodiments, the dummygate electrode layer is subjected to a planarization operation. Thedummy gate dielectric layer and the dummy gate electrode layer aredeposited using CVD, including LPCVD and PECVD, PVD, ALD, or othersuitable process. Subsequently, a mask layer is formed over the dummygate electrode layer. The mask layer can be a resist pattern or a hardmask pattern.

Next, a patterning operation is performed on the mask layer and dummygate electrode layer is patterned to form the dummy gate structures 40,as shown in FIGS. 5A and 5B. By patterning the dummy gate structures,the upper portions of the fin structures 21, which are to besource/drain regions, are partially exposed on opposite sides of thedummy gate structures, as shown in FIG. 5B. In this disclosure, a sourceand a drain are interchangeably used and the structures thereof aresubstantially the same. In FIG. 5B, two dummy gate structures 40 areformed on two fin structures 21, respectively, and one dummy gatestructure 40 is formed over two fin structures 21. However, the layoutis not limited to FIG. 5B.

The width of the dummy gate structures 40 in the X direction is in arange from about 5 nm to about 30 nm in some embodiments, and is in arange from about 7 nm to about 15 nm in other embodiments. A pitch ofthe dummy gate structures is in a range from about 10 nm to about 50 nmin some embodiments, and is in a range from about 15 nm to about 40 nmin other embodiments.

FIGS. 6A and 6B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure. FIG. 6A is a cross sectionalview corresponding to line Y2-Y2 of FIG. 6B.

After the dummy gate structures 40 are formed, a blanket layer of aninsulating material for sidewall spacers 45 is conformally formed byusing CVD or other suitable methods. The blanket layer is deposited in aconformal manner so that it is formed to have substantially equalthicknesses on vertical surfaces, such as the sidewalls, horizontalsurfaces, and the top of the dummy gate structures. In some embodiments,the blanket layer is deposited to a thickness in a range from about 2 nmto about 20 nm. In one embodiment, the insulating material of theblanket layer is different from the materials of the first isolationinsulating layer and the second isolation insulating layer, and is madeof a silicon nitride-based material, such as SiN, SiON, SiOCN or SiCNand combinations thereof. In some embodiments, the blanket layer(sidewall spacers 45) is made of SiN. The sidewall spacers 45 are formedon opposite sidewalls of the dummy gate structures 40, by anisotropicetching, as shown in FIGS. 6A and 6B.

FIGS. 7A and 7B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure. FIG. 7A is a cross sectionalview corresponding to line Y2-Y2 of FIG. 7B.

After the sidewall spacers 45 are formed, an interlayer dielectric (ILD)layer 50 is formed, as shown in FIGS. 7A and 7B. The materials for theILD layer 50 include compounds comprising Si, O, C and/or H, such assilicon oxide, SiCOH and SiOC. Organic materials, such as polymers, maybe used for the ILD layer 50. After the ILD layer 50 is formed, aplanarization operation, such as CMP, is performed, so that the topportions of the dummy gate electrode layers of the dummy gate structures40 are exposed.

FIGS. 8A and 8B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure. FIG. 8A is a cross sectionalview corresponding to line Y2-Y2 of FIG. 8B.

Next, as shown in FIGS. 8A and 8B, the dummy gate structures 40 areremoved, thereby forming gate spaces 48, in which the upper portions ofthe fin structures 21 (the second semiconductor layer 25 and at least apart of the first semiconductor layer 20) are exposed, respectively. Thesidewall spacers 45 are not removed.

The dummy gate structures can be removed using plasma dry etching and/orwet etching. When the dummy gate electrode layer is polysilicon and theILD layer 50 is silicon oxide, a wet etchant such as a TMAH solution canbe used to selectively remove the dummy gate electrode layer. The dummygate dielectric layer is thereafter removed using plasma dry etchingand/or wet etching.

FIGS. 9A-9C show one of the various stages of sequential processes formanufacturing a semiconductor device having a GAA FET according to anembodiment of the present disclosure. FIG. 9A is a cross sectional viewcorresponding to line Y2-Y2 of FIG. 9B, and FIG. 9C is a cross sectionalview corresponding to line X1-X1 of FIG. 9B.

In the gate spaces 48, the first semiconductor layer 20 is removed,thereby forming a space 19, as shown in FIG. 9A. When the firstsemiconductor layers 20 are Ge or SiGe and the second semiconductorlayers 25 and the substrate 10 are Si, the first semiconductor layers 20can be selectively removed using a wet etchant such as, but not limitedto, ammonium hydroxide (NH₄OH), tetramethylammonium hydroxide (TMAH),ethylenediamine pyrocatechol (EDP), or potassium hydroxide (KOH)solution. By removing the first semiconductor layer 20 in the gate space48, a semiconductor wire structure having a channel region is formed.Depending on the aspect ratio of the second semiconductor layer 25, thesemiconductor wire structure can also be referred to as a semiconductorfin structure.

FIGS. 10A and 10B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure. FIG. 10A is a cross sectionalview corresponding to line Y2-Y2 of FIG. 10B.

After the channel layer is formed, a gate dielectric layer 23 is formedover the channel region (second semiconductor layer 25) and thesurrounding areas, as shown in FIGS. 10A and 10B. In certainembodiments, the gate dielectric layer 23 includes one or more layers ofa dielectric material, such as silicon oxide, silicon nitride, or high-kdielectric material, other suitable dielectric material, and/orcombinations thereof. Examples of high-k dielectric material includeHfO₂, HfSiO, HfSiON, HfTaO, HfTiO, HfZrO, zirconium oxide, aluminumoxide, titanium oxide, hafnium dioxide-alumina (HfO₂—Al₂O₃) alloy, othersuitable high-k dielectric materials, and/or combinations thereof. Insome embodiments, the gate dielectric layer 23 includes an interfaciallayer formed between the channel layers and the dielectric material.

The gate dielectric layer 23 may be formed by CVD, ALD or any suitablemethod. In one embodiment, the gate dielectric layer 23 is formed usinga highly conformal deposition process such as ALD in order to ensure theformation of a gate dielectric layer having a uniform thickness aroundeach channel layer. The thickness of the gate dielectric layer 23 is ina range from about 1 nm to about 6 nm in one embodiment.

FIGS. 11A-12B show one of the various stages of sequential processes formanufacturing a semiconductor device having a GAA FET according to anembodiment of the present disclosure. FIG. 11B and FIG. 12B are thesame. FIG. 11A is a cross sectional view corresponding to line Y2-Y2 ofFIG. 11B, and FIG. 12A is a cross sectional view corresponding to lineY1-Y1 of FIG. 12B.

Subsequently, a gate electrode layer 60 is formed on the gate dielectriclayer 23. The gate electrode layer 60 includes one or more layers ofconductive material, such as polysilicon, aluminum, copper, titanium,tantalum, tungsten, cobalt, molybdenum, tantalum nitride, nickelsilicide, cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN, TaC, TaSiN, metalalloys, other suitable materials, and/or combinations thereof.

The gate electrode layer 60 may be formed by CVD, ALD, electro-plating,or other suitable method. The gate dielectric layer and the electrodelayer are also deposited over the upper surface of the ILD layer 50. Thegate dielectric layer and the gate electrode layer formed over the ILDlayer 50 are then planarized by using, for example, CMP, until the topsurface of the ILD layer 50 is revealed, as shown in FIG. 11A.

In certain embodiments of the present disclosure, one or more workfunction adjustment layers (not shown) are interposed between the gatedielectric layer 23 and the gate electrode layer 60. The work functionadjustment layers are made of a conductive material such as a singlelayer of TiN, TaN, TaAlC, TiC, TaC, Co, Al, TiAl, HfTi, TiSi, TaSi orTiAlC, or a multilayer of two or more of these materials. For then-channel FET, one or more of TaN, TaAlC, TiN, TiC, Co, TiAl, HfTi, TiSiand TaSi is used as the work function adjustment layer, and for thep-channel FET, one or more of TiAlC, Al, TiAl, TaN, TaAlC, TiN, TiC andCo is used as the work function adjustment layer. The work functionadjustment layer may be formed by ALD, PVD, CVD, e-beam evaporation, orother suitable process. Further, the work function adjustment layer maybe formed separately for the n-channel FET and the p-channel FET whichmay use different metal layers.

FIG. 12A shows the source/drain regions after the gate electrode layer60 is formed. As shown in FIG. 12A, the first semiconductor layers 20remain in the fin structure.

FIGS. 13A and 13B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure. FIG. 13A is a cross sectionalview corresponding to line Y1-Y1 of FIG. 13B.

As shown in FIGS. 13A and 13B, the ILD layer 50 is patterned by one ormore lithography and etching operations, thereby forming a firstsource/drain opening 58. In the first source/drain opening 58, thesecond semiconductor layer 25 and at least a part of the firstsemiconductor layer 20 are exposed.

In some embodiments, the second semiconductor layer 25, which becomes asource/drain region, is doped with appropriate dopants before or afterthe first source/drain opening 58 is formed. In other embodiments, oneor more epitaxial layers are formed over the second semiconductor layer25 before or after the first source/drain opening 58 is formed.

In FIGS. 13A and 13B, one source/drain opening 58 is formed to exposetwo fin structures. However, the configuration is not limited to this.In some embodiments, one source/drain opening 58 is formed over one finstructure, and in other embodiments, one source/drain opening 58 isformed over three or more fin structures.

FIGS. 14A and 14B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure. FIG. 14A is a cross sectionalview corresponding to line Y1-Y1 of FIG. 14B.

In the first source/drain openings 58, the first semiconductor layer 20is removed, thereby forming a space 27, as shown in FIG. 14A. When thefirst semiconductor layers 20 are Ge or SiGe and the secondsemiconductor layers 25 and the substrate 10 are Si, the firstsemiconductor layers 20 can be selectively removed using a wet etchantsuch as, but not limited to, ammonium hydroxide (NH₄OH),tetramethylammonium hydroxide (TMAH), ethylenediamine pyrocatechol(EDP), or potassium hydroxide (KOH) solution. By removing the firstsemiconductor layer 20 in the first source/drain opening 58, asource/drain region is separated from the substrate 10 (the bottomportion of the fin structure protruding from the substrate 10).

FIGS. 15A and 15B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toan embodiment of the present disclosure. FIG. 15A is a cross sectionalview corresponding to line Y1-Y1 of FIG. 15B.

Then, an insulating material layer 70 including one or more layers ofinsulating material is formed to fill the first source/drain opening asshown in FIG. 15A. The insulating material for the insulating materiallayer 70 is different from that of the ILD layer 50, and may includesilicon oxide, silicon nitride, silicon oxynitride (SiON), SiOCN, SiOC,SiCN, fluorine-doped silicate glass (FSG), or a low-k dielectricmaterial, formed by LPCVD (low pressure chemical vapor deposition),plasma-CVD, atomic layer deposition (ALD) or flowable CVD, or any othersuitable film formation methods. In some embodiments, the insulatingmaterial layer 70 includes SiCO or SiOCN. An anneal operation may beperformed after the formation of the insulating material layer 70.

FIGS. 16A-16C show one of the various stages of sequential processes formanufacturing a semiconductor device having a GAA FET according to anembodiment of the present disclosure. FIG. 16A is a cross sectional viewcorresponding to line Y1-Y1 of FIG. 16B, and FIG. 16C is a crosssectional view corresponding to line X1-X1 of FIG. 16B.

Then, the insulating material layer 70 is recessed, thereby forming asecond source/drain opening 72, as shown in FIGS. 16A and 16B. Since theinsulating material layer 70 is made of a different material than theILD layer 50, the insulating material layer 70 can be selectively etchedwith respect to the ILD layer 50. In certain embodiments, the insulatingmaterial layer 70 can be etched without a resist mask to expose theinsulating material layer 70 and to cover the ILD layer around theinsulating material layer 70.

The thickness H2 of the insulating material layer 70 under the secondsemiconductor layer 25 is substantially the same as the thickness of thefirst semiconductor layer 20, and is in a range from about 5 nm to about30 nm in some embodiments, and is in a range from about 10 nm to about20 nm in other embodiments. The thickness H3 of the insulating materiallayer 70 on the first isolation insulating layer 30 is in a range fromabout 2 nm to about 20 nm in some embodiments, and is in a range fromabout 5 nm to about 15 nm in other embodiments.

FIGS. 17A-17C show one of the various stages of sequential processes formanufacturing a semiconductor device having a GAA FET according to anembodiment of the present disclosure. FIG. 17A is a cross sectional viewcorresponding to line Y1-Y1 of FIG. 17B, and FIG. 17C is a crosssectional view corresponding to line X1-X1 of FIG. 17B.

After the insulating material layer 70 is recessed, in the secondsource/drain opening 72, a conductive material is formed. The conductivematerial is formed in and over the second source/drain opening 72 andthen a planarization operation, such as a CMP operation, is performed toform source/drain contacts 80, as shown in FIGS. 17A and 17B. Theconductive material includes one or more layers of Co, Ni. W, Ti, Ta,Cu, Al, TiN and TaN, or any other suitable material.

In some embodiments, a silicide layer 75 is formed over the secondsemiconductor layer 25 before forming the conductive material, as shownin FIGS. 18A and 18B. The silicide layer includes one or more of WSi,CoSi, NiSi, TiSi, MoSi and TaSi. When the second semiconductor layerincludes Ge, an alloy of Ge and metal (e.g., TiGe, NiGe, or CoGe) isformed, and when the epitaxial layer includes Si and Ge, an alloy of Si,Ge and metal (e.g., NiSiGe or TiSiGe) is formed. When the secondsemiconductor layer includes a Group III-V semiconductor, an alloy suchas Ni—InAlAs is formed.

It is understood that the GAA FET undergoes further CMOS processes toform various features such as contacts/vias, interconnect metal layers,dielectric layers, passivation layers, etc.

As shown in FIGS. 17A-18B, a bottom of the source/drain region (secondsemiconductor layer 25) is separated from the substrate 10 (a bottomportion of the fin structure protruding from the substrate 10) by theinsulating material layer 70 made of a different material than theisolation insulating layer 30 and the ILD layer 50. With this structure,the source/drain regions are electrically separated from the substrateand a parasitic transistor is not formed.

FIGS. 19A-23B show sequential processes for manufacturing asemiconductor device having a GAA FET according to another embodiment ofthe present disclosure. It is understood that additional operations canbe provided before, during, and after processes shown by FIGS. 19A-23B,and some of the operations described below can be replaced oreliminated, for additional embodiments of the method. The order of theoperations/processes may be interchangeable. Material, configuration,dimensions and/or processes the same as or similar to the foregoingembodiments described with respect to FIGS. 1A-18B may be employed inthe following embodiments, and detailed explanation thereof may beomitted.

In the foregoing embodiment, one channel layer (semiconductor wire) isformed from the fin structure. In the embodiments with respect to FIGS.19A-23B, multiple semiconductor wires vertically arranged are formedfrom one fin structure.

FIGS. 19A and 19B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toanother embodiment of the present disclosure. FIG. 19A is a crosssectional view corresponding to line Y1-Y1 of FIG. 19B.

FIGS. 19A and 19B correspond to FIGS. 13A and 13B after the firstsource/drain opening 58 is formed. As shown in FIG. 19A, the finstructure 121 includes multiple layers of first semiconductor layers 120and 122 and second semiconductor layers 125 alternately stacked. In oneembodiment, the first semiconductor layers 120 and 122 are made of SiGeand the second semiconductor layers 125 are made of Si. The first andsecond semiconductor layers are alternately epitaxially formed over thesubstrate 10 and the fin structures 121 are formed by patterningoperations performed similar to FIGS. 1A-2B as set forth above. In someembodiments, the thickness of the bottommost first semiconductor layer120 is greater than the thickness of the remaining first semiconductorlayers 122. Although FIG. 19A shows four second semiconductor layers125, the number of the second semiconductor layer can be two, three ormore than four.

FIGS. 20A and 20B show one of the various stages of sequential processesfor manufacturing a semiconductor device having a GAA FET according toanother embodiment of the present disclosure. FIG. 20A is a crosssectional view corresponding to line Y1-Y1 of FIG. 20B.

Then, similar to the operations explained with respect to FIGS. 14A-16B,the first semiconductor layers 120 and 122 are removed in the firstsource/drain opening 58, and the recessed insulating material layer 70is formed, as shown in FIG. 20A. In some embodiments, a space is formedbetween the bottommost second semiconductor layer 125 and the insulatingmaterial layer 70. In other embodiments, a part of the bottommost secondsemiconductor layer 125 is embedded in the insulating material layer 70.

FIGS. 21A-21C show one of the various stages of sequential processes formanufacturing a semiconductor device having a GAA FET according toanother embodiment of the present disclosure. FIG. 21A is a crosssectional view corresponding to line Y1-Y1 of FIG. 21B, and FIG. 21C isa cross sectional view corresponding to line X1-X1 of FIG. 21B.

Similar to the operations explained with respect to FIGS. 17A and 17B, asource/drain contact layer 80 is formed, as shown in FIGS. 21A and 21B.

In some embodiments, a silicide layer 75 is formed over the secondsemiconductor layers 125 before forming the conductive material, asshown in FIGS. 22A and 22B.

FIG. 23A is a cross sectional view corresponding to line Y2-Y2 of FIG.23B, which correspond to FIGS. 11A and 11B. As shown in FIG. 23A, aplurality of channel layers 125 are vertically arranged and each of thechannel layer 125 is wrapped by the gate dielectric layer 92 and thegate electrode layer 94.

Similar to the operations explained with respect to FIGS. 5A-11B, adummy gate structure is formed over the upper portion of the finstructure with stacked layers of the first and second semiconductorlayer. Then, a sidewall spacer is formed on opposing side faces of thedummy gate structure. Next, the dummy gate structure is removed, andthus a gate space surrounded by the sidewall space layer is formed, inwhich the upper portion of the fin structure is exposed. The firstsemiconductor layers are removed from the upper portion in the gatespace. By removing the first semiconductor layers, semiconductor wiresformed by the second semiconductor layers are obtained. A gatedielectric layer is formed to wrap the second semiconductor layers.Then, a metal gate electrode layer is formed over the gate dielectriclayer, thereby obtaining the structure of FIGS. 23A and 23B.

FIGS. 24A and 24B show a semiconductor device having a FinFET accordingto another embodiment of the present disclosure. Material,configuration, dimensions and/or processes the same as or similar to theforegoing embodiments described with respect to FIGS. 1A-23B may beemployed in the following embodiments, and detailed explanation thereofmay be omitted.

In this embodiments, a fin structure 25 formed by a second semiconductorlayer is employed as a channel region of a FET, as shown in FIG. 24A,while the source/drain structure has the same structure as shown in FIG.17 or 18 . The fin structure 25 is disposed over the first semiconductorlayer 20, which is not removed. It is understood that the GAA FETundergoes further CMOS processes to form various features such ascontacts/vias, interconnect metal layers, dielectric layers, passivationlayers, etc.

FIGS. 25A and 25B show correspondence between the simulation (model) andthe experiments. These figures show Id/Vg properties at Vds=−0.05 V and−0.65 V of a gate having Lg=70 nm with three vertically stacked Genanowire device (2-fin structure). FIG. 25A shows a linear plot and FIG.25B shows a log plot. Solid lines are experimental results and dots(black and white) are simulation results. It can be confirmed from FIGS.25A and 25B that the model for the simulation well reproduces the actualdevice behavior.

When a SiGe layer (a sacrificial layer) remains between the bottommostnanowire and the substrate (bottom fin), the isolation of the fin andthe nanowires is in sufficient. In contrast, in the foregoingembodiments, the SiGe layer is replaced with a dielectric layer 70.FIGS. 26A and 26B show the simulated Is/Vg properties at Vds=−0.05 V and−0.65V of a gate having Lg=30 nm with three vertically stacked Genanowire device (2-fin structure). FIG. 26A shows a linear plot and FIG.26B shows a log plot for the three individual NW FETs and the parasiticbottom FinFET. The subthreshold slope of the individual NW FETs is closeto the ideal 60 mV/dec, while the parasitic device has a much poorerslope. Accordingly, it can be understood that by isolating the fin bythe dielectric layer 70 can improve the device property.

FIGS. 27A and 27B shows off-current properties obtained by simulation.FIGS. 27A and 27B show hole current density maps of three verticallystacked Ge nanowire device at Lg=70 nm (FIG. 27A) and Lg=30 nm (FIG.27B) at Vg=0V and Vds=−0.65V (off-state conditions). In particular, atLg=30 nm, a high hole current density is observed in the parasiticbottom FinFET explaining the poor short channel effect control (i.e.,high subthreshold slope) leading to undesired high off-state leakage, atscaled gate lengths. Again, these figures show the necessity to removethe parasitic transistor from the stacked nanowire device. As set forthabove, in the FETs of the present disclosure, the source/drain regionsare isolated from the substrate (bottom fin) and thus no parasitictransistor exists.

The various embodiments or examples described herein offer severaladvantages over the existing art. For example, in the presentdisclosure, since an insulating material layer is inserted between thebottom of the source/drain region and the substrate (a protrudingportion of the substrate is a bottom of the fin structure), it ispossible to prevent formation of a parasitic transistor and to reduce anoff-state leakage current. Further, by using a different insulatingmaterial as the insulating material layer than the ILD layer and/or theisolation insulating layer, the process to form the insulating materiallayer becomes easier.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

In accordance with one aspect of the present disclosure, in a method ofmanufacturing a semiconductor device, a fin structure having a bottomportion, an intermediate portion disposed over the bottom portion and anupper portion disposed over the intermediate portion is formed. Theintermediate portion is removed at a source/drain region of the finstructure, thereby forming a space between the bottom portion and theupper portion. An insulating layer is formed in the space. Asource/drain contact layer is formed over the upper portion. Thesource/drain contact layer is separated by the insulating layer from thebottom portion of the fin structure. In one or more of the foregoing orfollowing embodiments, in the method, before the intermediate layer isremoved, a dielectric layer is formed over the fin structure, and thedielectric layer is patterned, thereby forming an opening in which theupper portion of the fin structure and at least a part of theintermediate portion of the fin structure are exposed. The intermediateportion is removed in the opening and the insulating layer is formed inthe opening. In one or more of the foregoing or following embodiments,the insulating layer and the dielectric layer are made of differentmaterial from each other. In one or more of the foregoing or followingembodiments, the insulating layer is made of SiCO. In one or more of theforegoing or following embodiments, the dielectric layer is made ofsilicon oxide. In one or more of the foregoing or following embodiments,the intermediate layer is made of Si_(x)Ge_(1-x) and the upper portionis made of Si_(y)Ge_(1-y), where x<y. In one or more of the foregoing orfollowing embodiments, the intermediate layer is made of Si_(x)Ge_(1-x),where 0.1<x<0.9, and the upper portion and the bottom portion are madeof Si.

In accordance with another aspect of the present disclosure, in a methodof manufacturing a semiconductor device, a fin structure having a bottomportion, an intermediate portion disposed over the bottom portion and anupper portion disposed over the intermediate portion is formed. Adielectric layer is formed over the fin structure. A metal gatestructure is formed over a channel region of the fin structure. Thedielectric layer is patterned, thereby forming an opening in which theupper portion of the fin structure and at least a part of theintermediate portion of the fin structure are exposed. The intermediateportion is removed at a source/drain region of the fin structure in theopening, thereby forming a space between the bottom portion and theupper portion. An insulating layer is formed in the space. Asource/drain contact layer is formed over the upper portion. Thesource/drain contact layer is separated by the insulating layer from thebottom portion of the fin structure. In one or more of the foregoing orfollowing embodiments, the metal gate structure is formed by thefollowing operations: a dummy gate structure is formed over the channelregion of the fin structure, a sidewall spacer is formed on opposingside faces of the dummy gate structure, the dummy gate structure isremoved, thereby forming a gate space surrounded by the sidewall spacelayer in which the channel region is exposed, a gate dielectric layer isformed over the exposed channel region, and a metal gate electrode layeris formed over the gate dielectric layer. In one or more of theforegoing or following embodiments, the exposed channel region includesthe upper portion of the fin structure and at least a part of theintermediate portion, and the intermediate portion is removed before thegate dielectric layer is formed. In one or more of the foregoing orfollowing embodiments, the insulating layer and the dielectric layer aremade of different material from each other. In one or more of theforegoing or following embodiments, the insulating layer, the dielectriclayer and the sidewall spacer layer are made of different material fromeach other. In one or more of the foregoing or following embodiments,the insulating layer is made of SiCO. In one or more of the foregoing orfollowing embodiments, the dielectric layer is made of silicon oxide. Inone or more of the foregoing or following embodiments, the intermediatelayer is made of Si_(x)Ge_(1-x) and the upper portion is made ofSi_(y)Ge_(1-y), where x<y. In one or more of the foregoing or followingembodiments, the intermediate layer is made of Si_(x)Ge_(1-x), where0.1<x<0.9, and the upper portion and the bottom portion are made of Si.

In accordance with another aspect of the present disclosure, in a methodof manufacturing a semiconductor device, a fin structure is formed. Thefin structure has a bottom portion, an intermediate portion disposedover the bottom portion and an upper portion disposed over theintermediate portion. The upper portion includes stacked layers of oneor more first semiconductor material layers and one or more secondsemiconductor layers. The intermediate portion are removed at asource/drain region of the fin structure, thereby forming a spacebetween the bottom portion and the upper portion. An insulating layer isformed in the space. A source/drain contact layer is formed over theupper portion. The source/drain contact layer is separated by theinsulating layer from the bottom portion of the fin structure. In one ormore of the foregoing or following embodiments, the one or more firstsemiconductor layers are removed from the upper portion when theintermediate portion is removed, and the source/drain contact layerwraps around the one or more second semiconductor layers. In one or moreof the foregoing or following embodiments, the bottom portion of the finstructure is embedded in an isolation insulating layer, and theinsulating layer and the isolation insulating layer are made ofdifferent materials from each other. In one or more of the foregoing orfollowing embodiments, in the method, a dummy gate structure is formedover the upper portion of the fin structure, a sidewall spacer is formedon opposing side faces of the dummy gate structure, the dummy gatestructure is removed, thereby forming a gate space surrounded by thesidewall space layer in which the upper portion is exposed, the one ormore first semiconductor layers are removed from the upper portion inthe gate space, a gate dielectric layer is formed to wrap the one ormore second semiconductor layers, and a metal gate electrode layer isformed over the gate dielectric layer.

In accordance with one aspect of the present disclosure, a semiconductordevice includes a semiconductor wire structure having a channel regionand a source/drain region. A source/drain contact layer is formed overthe source/drain region. The source/drain contact layer is embedded inan dielectric layer. An isolation insulating layer is disposed betweenthe dielectric layer and a substrate. A bottom of the source/drainregion is separated from the substrate by an insulating layer made of adifferent material than the isolation insulating layer and thedielectric layer. In one or more of the foregoing or followingembodiments, the insulating layer is made of SiCO. In one or more of theforegoing or following embodiments, the dielectric layer is made ofsilicon oxide. In one or more of the foregoing or following embodiments,the substrate includes a protrusion below the source/drain region, andthe insulating layer is disposed between the bottom of the source/drainregion and the protrusion. In one or more of the foregoing or followingembodiments, the source/drain region of the semiconductor wire structureand the protrusion are made of a same material. In one or more of theforegoing or following embodiments, the semiconductor device furtherincludes a gate structure including a gate dielectric layer and a metalgate electrode layer, and the gate dielectric layer wraps around thechannel region of the semiconductor wire structure. In one or more ofthe foregoing or following embodiments, a silicide layer is disposedbetween the source/drain region and the source/drain contact layer. Inone or more of the foregoing or following embodiments, a bottom of thesource/drain contact layer is separated from the isolation insulatinglayer by the insulating layer.

In accordance with another aspect of the present disclosure, asemiconductor device includes a first semiconductor wire structurehaving a channel region and a source/drain region, and a secondsemiconductor wire structure having a channel region and a source/drainregion. A source/drain contact layer is formed over the source/drainregion of the first semiconductor wire structure and the source/drainregion of the second semiconductor wire structure. The source/draincontact layer is embedded in a dielectric layer. An isolation insulatinglayer is disposed between the dielectric layer and a substrate. A bottomof the source/drain region of the first semiconductor wire structure anda bottom of the source/drain region of the second semiconductor wirestructure are separated from the substrate by an insulating layer madeof a different material than the isolation insulating layer and thedielectric layer. In one or more of the foregoing or followingembodiments, the insulating layer is made of SiCO and the dielectriclayer and isolation insulating layer are made of silicon oxide. In oneor more of the foregoing or following embodiments, the substrateincludes a first protrusion below the source/drain region of the firstsemiconductor wire structure and a second protrusion below thesource/drain region of the second semiconductor wire structure. Theinsulating layer is disposed between the bottom of the source/drainregion of the first semiconductor wire structure and the firstprotrusion and between the bottom of the source/drain region of thesecond semiconductor wire structure and the second protrusion. In one ormore of the foregoing or following embodiments, the first and secondsemiconductor wire structures and the substrate are made of a samematerial. In one or more of the foregoing or following embodiments, thefirst and second semiconductor wire structures and the substrate aremade of different materials. In one or more of the foregoing orfollowing embodiments, the semiconductor device further includes a firstgate structure including a gate dielectric layer and a metal gateelectrode layer, and a second gate structure including a gate dielectriclayer and a metal gate electrode layer, and the gate dielectric layer ofthe first gate structure wraps around the channel region of the firstsemiconductor wire structure, and the gate dielectric layer of thesecond gate structure wraps the channel region of the secondsemiconductor wire structure. In one or more of the foregoing orfollowing embodiments, a first silicide layer is disposed between thesource/drain region of the first semiconductor wire structure and thesource/drain contact layer, and a second silicide layer is disposedbetween the source/drain region of the second semiconductor wirestructure and the source/drain contact layer. In one or more of theforegoing or following embodiments, a bottom of the source/drain contactlayer is separated from the isolation insulating layer by the insulatinglayer.

In accordance with another aspect of the present disclosure, asemiconductor device includes semiconductor wire structures, which havea channel region and a source/drain region. A source/drain contact layeris formed over the source/drain region wrapping around the semiconductorwires. The source/drain contact layer is embedded in an dielectriclayer. An isolation insulating layer is disposed between the dielectriclayer and a substrate. A bottom of the source/drain region is separatedfrom the substrate by an insulating layer made of a different materialthan the isolation insulating layer and the dielectric layer. In one ormore of the foregoing or following embodiments, the insulating layer ismade of SiCO. In one or more of the foregoing or following embodiments,the substrate includes a protrusion below the source/drain region, andthe insulating layer is disposed between the bottom of the source/drainregion and the protrusion. In one or more of the foregoing or followingembodiments, the protrusion continuously extends from the substrate andis made of a same material as the substrate.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A semiconductor device, comprising: asemiconductor layer having a channel region, a source region and a drainregion disposed at ends of the channel region; a dielectric layer; asource contact layer embedded in the dielectric layer and disposed overthe source region; an isolation insulating layer disposed between thedielectric layer and a substrate; and a bottom fin structure protrudingfrom the substrate and embedded in the isolation insulating layer,wherein: the source region is disposed over the bottom fin structure,and a bottom of the source region is separated from the bottom finstructure by an insulating layer.
 2. The semiconductor device of claim1, wherein the insulating layer is made of a different material than theisolation insulating layer and the dielectric layer.
 3. Thesemiconductor device of claim 2, wherein the insulating layer is made ofSiCO.
 4. The semiconductor device of claim 2, wherein the dielectriclayer is made of silicon oxide.
 5. The semiconductor device of claim 1,wherein the source region of the semiconductor layer and the bottom finstructure are made of a same material.
 6. The semiconductor device ofclaim 1, further comprising: a gate structure including a gatedielectric layer and a metal gate electrode layer, wherein the gatedielectric layer wraps around the channel region of the semiconductorlayer.
 7. The semiconductor device of claim 1, wherein a silicide layeris disposed between the source region and the source contact layer. 8.The semiconductor device of claim 1, wherein the bottom of the sourcecontact layer is separated from the isolation insulating layer by theinsulating layer.
 9. A semiconductor device, comprising: a first bottomfin structure protruding from a substrate; a first semiconductor layerdisposed above the first bottom fin structure and having a channelregion, a source region and a drain region, which are disposed at endsof the channel region; a second bottom fin structure protruding from thesubstrate; a second semiconductor layer disposed above the second bottomfin structure and having a channel region, a source region and a drainregion, which are disposed at ends of the channel region; a sourcecontact layer disposed over the source region of the first semiconductorlayer and the source region of the second semiconductor layer; and aninsulating layer separating a bottom of the source region of the firstsemiconductor layer from the first bottom fin structure and separating abottom of the source region of the second semiconductor layer from thesecond bottom fin structure, wherein the source contact layer isdisposed on the insulating layer.
 10. The semiconductor device of claim9, further comprising: an isolation insulating layer disposed on thesubstrate a dielectric layer disposed on the isolation insulating layer,in which the source contact layer is disposed, wherein the insulatinglayer is made of a different material than the isolation insulatinglayer and the dielectric layer.
 11. The semiconductor device of claim 9,wherein the insulating layer is made of SiCO.
 12. The semiconductordevice of claim 9, the first and second semiconductor layers and thesubstrate are made of a same material.
 13. The semiconductor device ofclaim 9, the first and second semiconductor layers and the substrate aremade of different materials.
 14. The semiconductor device of claim 9,further comprising: a first silicide layer disposed between the sourceregion of the first semiconductor layer and the source contact layer,and a second silicide layer is disposed between the source region of thesecond semiconductor layer and the source contact layer.
 15. Thesemiconductor device of claim 10, wherein a bottom of the source contactlayer is separated from the isolation insulating layer by the insulatinglayer.
 16. A semiconductor device, comprising: an isolation insulatinglayer disposed over a substrate; a semiconductor layer disposed over thesubstrate and having a channel region, a source region and a drainregion disposed at ends of the channel region; a dielectric layerdisposed over the isolation insulating layer; a source contact layerembedded in the dielectric layer and disposed over the source region;and an insulating layer disposed between a bottom of the source regionand the substrate, and between a bottom of the source contact layer andthe isolation insulating layer, wherein the insulating layer includes aprotrusion protruding toward the substrate and embedded in the isolationinsulating layer.
 17. The semiconductor device of claim 16, wherein theinsulating layer is made of SiCO.
 18. The semiconductor device of claim16, wherein a liner insulating layer is disposed between the protrusionand the isolation insulating layer.
 19. The semiconductor device ofclaim 16, wherein a bottom of the source contact layer is separated fromthe isolation insulating layer by the insulating layer.
 20. Thesemiconductor device of claim 16, wherein a silicide layer is disposedover the source region and is in contact with the insulating layer.